Rickettsiae
| Rickettsiae | ||||||||||||
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Rickettsia rickettsii in the host cell |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Rickettsia | ||||||||||||
| da Rocha-Lima 1916 |
Rickettsia ( bacteria of the genus Rickettsia ) are globally occurring organisms that are now counted among the bacteria, which are found in many ticks , fleas , mites and lice and for which these serve as vectors (carriers).
In humans (endemic in Mediterranean countries, Eastern Europe, the tropics and North America) they cause a whole range of diseases with different clinical pictures, which are medically grouped under the group of rickettsioses . Examples are spotted fever (syn. Typhus exanthematicus), Volhynian fever (trench fever ), rickettsial pox , Brill-Zinsser disease , Boutonneuse fever (Mediterranean tick spotted fever ) and Rocky Mountain spotted fever . Like viruses , rickettsiae thrive as intracellular parasites only in living cells . In this way they manage to evade the immune system of their hosts. The term "rickettsiae" is often used for all members of the order of the rickettsiales .
These organisms were named Rickettsiae in honor of the pathologist Howard Taylor Ricketts , who researched, among other things, the Rocky Mountains spotted fever, the pathogen of which he was able to detect in the blood of infected people and in the cattle tick species active as a vector . In 1909 he traveled to Mexico City with the aim of researching typhus . He became infected with rickettsiae, fell ill and died in 1910.
Typical symptoms of rickettsiosis are fever, headache and rash. The diagnosis is usually made serologically .
The majority of all rickettsiae are sensitive to antibiotics of the tetracycline group ; In an appropriate case, an infection can be treated with a two-week dose of doxycycline . Quinolones are also used as an alternative . For infections of the central nervous system, chloramphenicol or (the tetracycline) doxycycline in combination with quinolones and / or rifampicin can be used as antimicrobial drugs. In moist media, destruction takes place at 50 ° C. in 15 minutes. Even with conventional disinfectants the leave pathogens effectively destroy.
properties
Rickettsiae are gram-negative , highly diverse (polymorphic, pleomorphic) organisms that do not form spores . Often they are round ( cocci ) to oval bacteria with a diameter of 0.1 µm ; they can also appear as rods (1–4 μm long) or thread-like (10 μm long). Occasionally they form chains, but mostly they appear singly or in pairs. The survival of the obligatory intracellular rickettsiae depends entirely on their eukaryotic host cell (mostly endothelial cells ), into whose cytoplasm they have to penetrate in order to be protected from the host's defense system. The multiplication by transverse division also takes place inside the host cell. The bacteria are then released by constriction from the cell membrane ( exocytosis ) or by lysis , which destroys the host cell. At least R. conorii is capable of movement within the host cell.
Due to their dependence on the host cell, the bacteria can not be kept in artificial culture media in the laboratory . They are therefore grown either in biological tissues or in embryo cultures (typically chicken embryos are used). Because of their cell dependency and their reduced metabolism , rickettsiae were often grouped as microorganisms somewhere between the viruses and the larger real bacteria , as an "intermediate species", as it were. For a long time they were also referred to as "big viruses".
Mechanism of Cell Invasion
How rickettsiae manage to penetrate eukaryotic cells has so far been a mystery. At the end of 2005 , scientists from the Pasteur Institute in Paris succeeded in identifying two key proteins involved in the penetration process using Rickettsia conorii . These are the bacterial protein rOmpB and the mammalian protein Ku70 , which is normally found in the nucleus of mammalian cells . Obviously, however, it can also migrate to the cell membrane , where it is held by the Rickettsial rOmpB and used to penetrate the cell. Because of this “telltale” property, the scientists also called Ku70 the “molecular stooge” of the rickettsiae.
Endosymbiotic Theory
The species Rickettsia prowazekii is of particular interest in the endosymbiotic theory with regard to the mitochondria . Mitochondria with the largest genome known to date were found in the single cell Reclinomonas americana . It is therefore assumed that this mitochondrion still has the greatest genetic similarity to the original symbiont . When comparing bacteria with the mitochondrial DNA of this unicellular organism, the fully sequenced genome of Rickettsia prowazekii showed the greatest agreement. So it can be assumed that Rickettsia is closely related to the ancestor of the mitochondria.
However, this assumption is not considered certain. The genome of Rickettsia prowazekii , like the genome found in the mitochondria, is very small. Both have presumably shrunk in the billions of years of evolution, which is why a strong similarity in the gene structure does not allow a clear statement. So could z. B. Rickettsia and the original bacterium that formed the symbiont also descended from a common ancestor.
grouping
With regard to their property as human pathogens , rickettsiae are usually divided into the following three groups:
| organism | caused disease | Occurrence |
|---|---|---|
| R. rickettsii | Rocky Mountains spotted fever | western hemisphere |
| R. akari | Rickettsial smallpox | USA , former Soviet Union |
| R. conorii |
Boutonneuse fever mild course: lymphadenitis , pronounced primary lesion , exanthem |
Mediterranean countries , Africa , Southwest Asia , India |
| R. africae | African tick bite fever ( African tick bite fever ) | Africa south of the Sahara , French Antilles |
| R. felis | Flea spotted fever (Syn. Cat flea typhus) | worldwide |
| R. sibirica | Sibirian tick typhus ("North Asian or Siberian tick bite fever ") | Siberia , Mongolia , Northern China |
| R. australis | Australian tick typhus ("Australian tick bite fever") | Australia |
| R. japonica | Japanese spotted fever | Japan |
| organism | caused disease | Occurrence |
|---|---|---|
| R. prowazekii | Classic typhus exanthematicus , Brill-Zinsser disease , classic typhus | worldwide |
| R. typhi | murine typhus (endemic typhus) | worldwide |
| organism | caused disease | Occurrence |
|---|---|---|
|
O. tsutsugamushi (now a genus of its own , Orientia ) |
Tsutsugamushi fever ( scrub typhus ); severe course: encephalitis , lymphadenitis , pronounced primary lesion , rash |
Southwest Asia , Northern Australia , Pacific Islands |
Systematics
The following species are grouped together in the genus Rickettsia :
- Rickettsia aeschlimannii Beati et al. 1997
- Rickettsia africae Kelly et al. 1996
- Rickettsia akari Huebner et al. 1946
- Rickettsia asiatica Fujita et al. 2006
- Rickettsia australis Philip 1950
- Rickettsia bellii Philip et al. 1983
- Rickettsia canadensis corrig. McKiel et al. 1967
- Rickettsia conorii Rumps 1932
- Rickettsia felis Bouyer et al. 2001, emend. La Scola et al. 2002
- Rickettsia heilongjiangensis Fournier et al. 2006
- Rickettsia helvetica Beati et al. 1993
- Rickettsia honey Stenos et al. 1998
- Rickettsia japonica Uchida et al. 1992
- Rickettsia massiliae Beati & Raoult 1993
- Rickettsia montanensis corrig. (ex Lackman et al. 1965) Weiss & Moulder 1984
- Rickettsia parkeri Lackman et al. 1965
- Rickettsia peacockii Niebylski et al. 1997
- Rickettsia prowazekii da Rocha-Lima 1916 ( type species )
- Rickettsia raoultii Mediannikov et al. 2008
- Rickettsia rhipicephali (ex Burgdorfer et al. 1978) Weiss & Moulder 1988
- Rickettsia rickettsii (Wolbach 1919) Rumps 1922
- Rickettsia sibirica Zdrodovskii 1948
- Rickettsia slovaca Sekeyová et al. 1998
- Rickettsia tamurae Fournier et al. 2006
- Rickettsia typhi (Wolbach & Todd 1920) Philip 1943
literature
- Karl Wurm, AM Walter: Infectious Diseases. In: Ludwig Heilmeyer (ed.): Textbook of internal medicine. Springer-Verlag, Berlin / Göttingen / Heidelberg 1955; 2nd edition, ibid. 1961, pp. 9-223, here: pp. 154-160 ( Rickettsiosen ).
- Rickettsia gene code cracked. New insights into the evolution of multicellular cells . In: Berliner Zeitung , November 18, 1998.
- Marianne Abele-Horn: Antimicrobial Therapy. Decision support for the treatment and prophylaxis of infectious diseases. With the collaboration of Werner Heinz, Hartwig Klinker, Johann Schurz and August Stich, 2nd, revised and expanded edition. Peter Wiehl, Marburg 2009, ISBN 978-3-927219-14-4 , p. 225 ( rickettsiosis ).
Web links
Individual evidence
- ↑ Marianne Abele-Horn (2009), p. 225.
- ^ Marianne Abele-Horn (2009).
- ↑ H. Ogata et al .: Mechanisms of evolution in Rickettsia conorii and R. prowazekii. In: Science , 2001 Sep 14,293 (5537), pp. 2093-2098, PMID 11557893 .
- ↑ JJ Martinez et al .: Ku70, a Component of DNA-Dependent Protein Kinase, Is a Mammalian Receptor for Rickettsia conorii. In: Cell . Vol. 123, 2005, pp. 1013-1023, PMID 16360032 .
- ↑ David N. Fredricks: Introduction to the Rickettsiales and Other Intracellular Prokaryotes . In: Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer, Erko Stackebrandt (eds.); The Prokaryotes, A Handbook of the Biology of Bacteria . 7 volumes. 3. Edition. Springer-Verlag, New York a. a. 2006, ISBN 0-387-30740-0 . Vol. 5: Proteobacteria: Alpha and Beta Subclasses , ISBN 0-387-25495-1
- ↑ N. Roch, O. épaulard, I. Pelloux, P. Pavese, JP Brion, D. Raoult, M. Maurin: African tick bite fever in elderly patients: eight cases in French tourists returning from South Africa. In: Clinical infectious diseases: an official publication of the Infectious Diseases Society of America. Volume 47, number 3, August 2008, pp. E28 – e35, ISSN 1537-6591 . doi: 10.1086 / 589868 . PMID 18558881 . (Review).
- ^ Didier Raoult, Philippe Parola: Rickettsial Diseases. CRC Press, 2007, ISBN 9781420019971 , pp. 87-93.
- ↑ N. a. Jia, Jia-Fu Jiang et al. a .: Rickettsia sibirica Subspecies sibirica BJ-90 as a Cause of Human Disease. In: New England Journal of Medicine. 369, 2013, pp. 1176–1178, doi: 10.1056 / NEJMc1303625 .
- ↑ JP Euzéby: List of Prokaryotic Names with Standing in Nomenclature. ( Genus Rickettsia ( Memento of the original dated December 6, 2006 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. )
